1. Field of the Invention
The present invention relates generally to loudspeaker enclosures, and more particularly to a high-fidelity loudspeaker enclosure having a stacked construction to provide a shaped acoustic chamber and isolation between the individual drivers in a multiple driver speaker.
In the field of high-fidelity music reproduction, substantial efforts have been made to obtain sound reproduction which is as faithful as possible to the original recorded sound. In most systems, tones are reproduced by individual diaphragms which are moved by a combination of permanent magnets and voice coils through which electrical signals are passed. The individual diaphragms with their magnetic and electrical apparatus are referred to as drivers. Unfortunately, each driver is capable of faithfully reproducing sound within only a limited frequency range. For this reason, modern high-fidelity speaker enclosures incorporate a number of individual drivers, which together cover the full audio spectrum.
The sound quality of a speaker system depends on both the drivers and the structure supporting the drivers. Each driver in a speaker system moves two masses of air. The first mass, in front of the diaphragm, vibrates with the intended frequencies to produce the desired tones. The second mass, behind the diaphragm, also vibrates with similar frequencies. However, the soundwaves which propagate from the back of a driver are out of phase with the intended sound reproduction, and unless carefully controlled, can significantly distort the sounds produced. It is for this reason that the rear surfaces of drivers are generally surrounded by speaker enclosures.
Although multiple driver speaker enclosures do successfully reproduce music with acceptable quality, there are at least two factors which have limited the quality of sound reproductions. The first factor is that speaker drivers, when combined with standard speaker enclosures, result in systems which have inherent resonant frequencies. This problem is most acute for lower frequency sounds, producing unnatural "booming," an emphasis on particular bass tones at specific frequencies. Much of this distortion is produced by the flat parallel surfaces of conventional speaker cabinet enclosures. The radiating soundwaves within such enclosures strike these flat surfaces, bouncing back and forth between them, and thereby causing standing waves within the enclosure. These standing waves interfere with the proper operation of the speaker in response to various frequencies. Efforts have been made to tailor the enclosures to the drivers by having baffled ports, known as "bass reflex," or alternatively by sealing the enclosure, known as "acoustic suspension." Nonetheless, non-linear response characteristics caused by intermodulation can be quite noticeable, even in the best of conventional speaker systems.
The second problem which has limited the quality of sound reproduction with conventional speaker enclosures is the interaction between the individual drivers of a multiple driver speaker system. As noted above, multiple drivers are required to reproduce the full spectrum of the audio range. As different drivers are moving at different frequencies, the vibrations set up by an individual driver on a speaker enclosure may well interfere with an alternate driver vibrating in an alternate frequency range which shares the same acoustic chamber. Moreover, vibrations also propagate through the speaker structure, so that drivers having chambers which are isolated by a simple baffle will still suffer the effects of the adjacent driver producing an alternate frequency.
The problems which are presented by conventional speaker enclosures have been recognized in the past, and attempts have been made to overcome them. To avoid establishing standing waves within a parallel wall speaker enclosure, speaker enclosures have been manufactured having a spherical or elliptical acoustic chamber behind the speaker. By using such curved inner surfaces in the speaker interior, the development of standing waves within the enclosure has been minimized. To improve the isolation between drivers in a multiple driver speaker system, separate speaker enclosures have been used specifically for the bass drivers. Unfortunately, music recordings are generally engineered for reproduction by two-speaker stereo systems, and further separation of the sound source is often undesirable. Alternatively, large, heavy speaker enclosures having walls between the individual drivers of sufficient mass to reduce vibration passed between chambers have also been constructed.
These prior art approaches at overcoming the limitations of speaker fidelity have met with only limited commercial success. The difficulty in constructing shaped speaker enclosures, together with the sound source separation and space use problems of a multiplicity of individual speaker enclosures, have limited the commercial acceptance of these prior art approaches.
For the above reasons it would be desirable to provide a speaker construction which would allow tailoring of the individual driver chambers. It would be particularly desirable if such construction techniques would further allow isolation between individual driver chambers within a multiple driver speaker enclosure. It would be best if such techniques did not require expensive or exotic materials or machining, and if the resulting speaker enclosures did not require any additional space.
2. Description of the Background Art
U.S. Pat. No. 4,591,020, issued to Hruby, Jr., describes a speaker enclosure having first and second interconnected chambers. The first chamber may be formed from a plurality of adjacent panels. The panels each have central openings that combine to form a cylindrical interior volume. U.S. Pat. No. 4,281,738, issued to Jackson, describes a spherical speaker enclosure for a single bass driver. U.S. Pat. No. 4,437,541, issued to Cross, describes a controlled dispersion speaker having a plurality of baffles.
U.S. Pat. No. 3,779,337, issued to Gregory, describes a speaker mount assembly having alternate layers of rigid blocks and vibration damping material. U.S. Pat. No. 4,569,414, issued to Fulton, describes a speaker system having a plurality of individual driver enclosures which are separated by a vibration damping material. U.S. Pat. No. 4,130,174, issued to Ostrander et al., describes a speaker formed with blocks of open cell foam and a thin pad of closed cell foam to provide isolation between drivers. U.S. Pat. Nos. 3,720,285 and 1,997,790 are also generally of interest.